1. Field of the Invention
The present invention relates to methods and related components for suspending an electric submergible pumping system ("ESP") within a wellbore and, more particularly, to methods and related components for disposing an electric power cable within a conduit to which is attached the ESP.
2. Description of Related Art
To reduce the size of equipment and the associated costs needed to deploy and recover an electric submergible pumping system ("ESP") within a wellbore, ESP's can be suspended from coiled tubing, rather than conventionaljointed tubing. This method takes advantage of the relatively low cost and ease of transportation of the units used to install and remove coiled tubing. Typical arrangements for suspending an ESP on coiled tubing are disclosed in U.S. Pat. Nos. 3,835,929; 4,830,113; and 5,180,014.
The electric power cable that is used to connect an electric motor of the ESP to a surface power source does not have sufficient internal strength to support its own weight over about twenty (20) feet. Therefore, the cable is clamped, banded or strapped to the outside of the jointed tubing or the coiled tubing at intervals, as disclosed in U.S. Pat. No. 4,681,169. Alternatively, the cable can be disposed within the coiled tubing, as disclosed in U.S. Pat. Nos. 4,336,415; 4,346,256; 5,145,007; 5,146,982; and 5,191,173.
When the cable is disposed within the coiled tubing, standoff devices are often used to centralize the cable within the coiled tubing. These prior standoff devices also support the cable, in place of the prior external clamps or straps, by preventing longitudinal movement of the cable with respect to the coiled tubing and thereby transfer the weight of the cable to the coiled tubing. These standoff devices are usually referred to as cable anchors, and examples thereof are disclosed in U.S. Pat. Nos. 5,193,614; 5,269,377; and 5,435,351.
Common problems associated with cable anchors are as follows. The cable and the coiled tubing have very different coefficients of thermal expansion, so that when the cable thermally expands after exposure to well conditions it is rigidly held by the cable anchors, and as such stress-related failures occur within the cable. Some prior cable anchors are relatively mechanically complex, and require injection of a solvent to release and set the anchors. Some cable anchors require a time consuming and uncontrollable chemical interaction to cause elastomeric materials on the cable or in the cable anchors to swell, and thereby frictionally engage the interior of the coiled tubing. Also, cable anchors tend to slip over time, so the cable extends longitudinally, which can damage or break the copper conductors. When coiled tubing has been used several times, it tends to no longer retain its circular cross-section but becomes slightly flattened or "oval" in shape. Internal cable anchors used in this oval coiled tubing have tendency to not consistently lock in place. In addition, the cable will be compressed against the lowermost electrical connector. This cable compression has caused electrical connectors to fail, necessitating the costly removal of the ESP from the well. Compounding the problem, the cable anchors often are very difficult to release to permit the removal of the cable from the coiled tubing.
There is a need for a simple method and related components for quickly and predictably disposing an electric power cable within a conduit, such as coiled tubing, that does not need cable anchors or other devices to transfer the weight of the cable to the conduit.